Protesters in London demand justice for the 96 victims of the Hillsborough tragedy in 2009. Photograph: Anthony Devlin/PA

Police officers sexually harassed a vulnerable Hillsborough survivor and threatened others with criminal charges if they did not alter statements, according to fresh allegations into the conduct of the authorities following the tragedy.

One officer pestered a young woman for sex only weeks after the disaster, while other witnesses were reportedly threatened with jail if they did not change accounts that portrayed the police in a negative light.

Speaking publicly for the first time, Diane Lynn, 45, has described how a West Midlands officer grabbed her and repeatedly asked her to come back to his hotel for sex following an official witness interview a few weeks after the disaster that killed 96 people in April 1989.

Lynn, then a 22-year-old student nurse who was suffering from severe shock after witnessing the fatal crush, said she had not come forward previously because she thought no one would believe her. However, the recent findings of the Hillsborough Independent Panel, which exposed the extent of the police cover-up, had persuaded her that her account would be taken seriously.

In May 1989, plainclothes West Midlands officers, appointed to investigate the role of the South Yorkshire force at Hillsborough, interviewed Lynn and her brother as they collected statements from supporters present at the FA Cup semi-final. She said: "Afterwards they said, 'Do you want to show us around Liverpool?', and I said, 'No problem at all'. I thought it was a friendly thing to do, I love my city."

Although still traumatised, Lynn hoped that going out might assist a return to normality. "The officer was 40-odd, I was 22 – that was why I felt safe; plus I don't get drunk ever," she said.

However, later when she was showing the officer where to catch a taxi, his mood changed. Lynn said: "He started putting his arm around me, saying, 'Come back to my hotel, come back.' I knew he had a wife because he had mentioned it earlier in the conversation, but he said, 'My wife will never know.' I felt very uncomfortable, extremely uncomfortable, I just had to get out and ran. He wasn't happy."

Lynn, now married and a nurse living in Liverpool, said: "I was still in shock at the time, I was in a very bad place. Everything was not right. It wasn't until December [that year] that I realised I had post-traumatic stress. I still cry about it a lot, the way people were treated.

"I felt no one was listening to us, I never told anyone about it because people just think you've led them on, it's not what I'm like. In those days no one was going to believe you against the police."

At the time the police cover-up was under way, with recently disclosed evidence indicating that West Midlands police were part of a broader plot to blame the supporters and disguise the failings of the South Yorkshire force. Meanwhile, further fresh allegations reveal that West Midlands officers threatened survivors with criminal charges if they refused to retract statements that criticised police.

Chartered accountant Nick Braley, 43, said: "[The lead investigating officer] told me he would be checking if I had a criminal record and that I would be charged with wasting police time."

During his interview Braley, then a 19-year-old student at Sheffield City Polytechnic, refused to agree he had seen Liverpool fans breaking into the ground. He told West Midlands officers that police were helping push fans over the fence to alleviate a crush outside the stadium.

Braley said: "He spent a long time contesting my assertion that I had not witnessed 'unauthorised entry'. Later he wrote 'witnessed unauthorised entry' on my statement without my consent – that was absolutely not what I said."

In addition, Braley says his official police statement also omits several of his key assertions, including how police pushed fans back into the fatal crush and that the tenor of the interview was overtly political.

"The main interviewer decided early on in my interview that I was a "leftwing agitator who was out to get the police. He questioned if I was in the Socialist Workers' party or the Workers' Revolutionary party," he said.

The officer questioned whether Braley– an Ipswich fan who went to the match as a neutral with friends who were Liverpool supporters – was even at the game. "He disputed my attendance, saying my lack of injuries – bruised ribs and arm – were not enough given the greater injuries of other fans."

Since the Observer reported that survivors were bullied to change their statements as well as police, it has emerged that "significant" numbers of fans at Hillsborough have come forward to warn investigators that their witness statements were altered. Both the Independent Police Complaints Commission and the director of public prosecutions, Keir Starmer, are conducting inquiries into possible crimes committed by police.

Parliament heard last week that the IPCC has been given a preliminary list of names of 1,444 officers currently serving with South Yorkshire police, although officials admit the true figure is likely to be nearer 2,444.